Working in batches, carefully ladle parsnip mixture into blender. Cover, with center part of blender cover removed to allow steam to escape (drape with clean kitchen towel to avoid splatter), and blend until smooth. (Blended soup can be covered and refrigerated up to 1 day.) Place blended soup in saucepot and reheat on medium-low until hot, adding additional water if you prefer a thinner soup. Stir in 1/2 teaspoon salt and 1/4 teaspoon freshly ground black pepper.